1. Field of the Invention
The present invention relates to an electronic apparatus used for the internal combustion engine, specifically, to a laminated structure in the semiconductor switching devices.
2. Description of the Prior Art
In the prior art, Beryllia is used for reducing the heat generation from the power transistors in order to reduce the heat resistance, in which the life-time elongation technology for the laminated structure is not used and, in some cases, there is no consideration for the long-time guarantee to be required for the automotive parts.
For example, one of this kind of electronic apparatus is described in the Japanese Patent Application Laid-Open No. 3-30440(1991).
In the prior art apparatus, in order to release efficiently the heat generated by the semiconductor switching device, Beryllia is selected for the material used for the electric insulation plate. In these devices, a refractory metal is used for the solder as the bonding between the beryllia and the metallic heat sink, and the bonding between the semiconductor switching devices. In case that the atmospheric conditional change and the repetitive stress due to the self heat generation occur, the stress is applied to the solder bonding parts, and the crack arises in the solder bonding parts, and consequently, there might be the catastrophic breakdown in the solder bonding parts. And furthermore, in the prior art, the laminated structure is formed in a single module, and the dispersion in the structural and material property of the solder bonding parts could be made to be as small as possible. However, in case that a plurality of laminated layers are formed in a single module, what makes problems is that the dispersion in the manufacturing quality of the solder bonding parts may become greater and the fraction of the defective parts may increase.
The object of the present invention is to provide an ignition apparatus for the inner combustion engine with high reliability in its device bonding parts.
In the present invention, the material is selected so as to be used for the solders for bonding the semiconductor switching device and the beryllia, and for bonding the beryllia and the metallic heat sink. In general, as there may be a case that the temperature due to the heat generation by the switching devices reaches as high as 100xc2x0 C. to 350xc2x0 C., refractory metal is used as the solder. The solder having lower melting point is used generally for the bonding under the beryllia so that the difference xcex1 in the thermal expansion coefficient between the metallic heat sink and the beryllia may be compensated. In case that the difference xcex1 is already within 0.000001/xc2x0 C., general purpose standard solder materials are used for the bonding. In case that the difference xcex1 is over 0.000001/xc2x0 C., nonstandard long-life solder materials are used. By keeping the thickness of the solder bonding layer between the heat sinks and between the switching devices, respectively, greater than from t0.05 mm to t0.2 mm, it can be respected that the dispersion in the manufacturing process and the fraction of the defected parts may be reduced.
In controlling the component and the thickness of the solder materials, for example, as for solder including refractory metal, what may be used includes solder with Pb:Sn=90:10, solder with Pb:Sn=80:20, solder including antinomies metal, and solder including Ag. As for solder with lower melting point, what can be used includes solder including eutectic materials, and solder with Pb:Sn=50:50. In addition, for the lifetime elongation of the solder bondings, the thickness control is used. For example, refractory metal is used for the solder bonding under the switching device, and solder including eutectic materials or high-temperature solder can be used for the solder bonding under the beryllia. In case of using FE for the metallic heat sink, the lifetime elongation can be established without serious control of the thickness of the solder bondings, because of the lower difference xcex1 in the thermal expansion coefficient. In case of using Cu or Al for the metallic heat sink, it is required to control seriously the thickness of the solder bondings. In case of using solder materials with Pb:Sn=90:10 for the solder materials under the switching devices, in general, it will be appreciated that the thickness of the solder bonding to be kept over 0.05 mm can contribute to the elongation of the lifetime.